1. Field of the Invention
The invention relates to a process for preparing alpha,omega-dicarboxylic acids or esters thereof by ozonolysis and subsequent oxidation.
2. Description of the Related Art
Ozonolysis in the context of the invention is understood to mean the cleavage of a carbon-carbon double bond by the action of ozone. According to the mode of workup, carbonyl compounds, alcohols or carboxylic acids may be obtained.
alpha,omega-Dicarboxylic acids are understood to mean carboxylic acids with two carboxyl groups, the carbon chain being substituted by a carboxyl group at position 1 and at the terminal position.
The ozonolysis of olefins is an important method for preparation of carboxylic acids, aldehydes and alcohols (Baily, P. S., Ozonation in Organic Chemistry, Academic: New York, N.Y., 1978, Vol. 1.). At the core of this reaction type is the 1,3-dipolar cycloaddition of ozone onto a C,C-double bond of an olefin (1) to form the primary ozonide (1,2,3-trioxolane, 2). This species is an unstable intermediate which decomposes directly to an aldehyde fragment (3) and a carbonyl oxide (4) (scheme 1).

The carbonyl oxide can firstly polymerize or dimerize to give a 1,2,4,5-tetraoxolane (5), or recombine in a further cycloaddition to give a secondary ozonide (1,2,4-trioxolane, 6). Proceeding from compound 6, it is possible to prepare aldehydes (7, 8) via a reductive workup, or carboxylic acids (9, 10) via an oxidative workup (Kropf, H., Houben-Weyl Methoden Der Organischen Chemie (Methods of Organic Chemistry); Kropf H. ed.; Georg Thieme: Stuttgart, 1988; Vol. E13/2, p. 1111.; Smith, M. B., March, J. March's Advanced Organic Chemistry; John Wiley & Sons, Inc; 2001, 5th ed., p. 1522). The aldehydes in turn can be reduced further to the alcohol.
A significant disadvantage of this reaction sequence is the formation of the usually explosive secondary ozonides, polymeric peroxides or 1,2,4,5-tetraoxolanes, some of which are stable compounds and can thus accumulate in downstream reaction and workup steps and constitute a considerable risk (Kula, J. Chem. Health Saf. 1999, 6, 21; Gordon, P. M. Chem. Eng. News 1990, 68, 2). Furthermore, in the case of an oxidative or reductive workup of secondary ozonides, one oxidation or reduction equivalent must be used (oxygen, hydrogen peroxide, or dimethyl sulphide, triphenylphosphine, etc.).
A further problem occurs in the oxidation reaction. If the oxidation is performed at relatively low temperatures, it proceeds very slowly, but an increase in the temperature leads to increased formation of by-products which have to be removed in a complex manner in further process steps. One example of such further processing is chain degradation by decarboxylation.